The invention relates to a method of automatically adjusting the die height of a press having plural dies.
FIG. 5 shows a conventional device for automatically adjusting a slide of a press. In the drawing, a connecting rod 1 is connected to a crank portion of a press crankshaft (not shown). A slide point portion 3 of the press links the connecting rod 1 to a slide 8. At the slide point portion 3, there is provided a ball or wrist pin, not shown. The connecting rod 1 and the slide point portion 3 are adjustably connected by an adjustment screw 4 which is rotated by a worm wheel 5 and a worm gear 6 to adjust the axial spacing of the connecting rod 1 and the slide 8.
The worm gear 6 is rotated by a drive shaft 12a, which is connected to a deceleration motor 11. A slide position adjustment unit 20 comprises a slide position setting element or means 21, a down controller 22, a slide adjustment actuator (e.g. button means) 23a, an up controller 24 and a change-over element or means 25 by which the controllers 22, 24 are selected.
A device 9 for confirming that the slide 8 has reached an upper limit is formed as a limit switch which operates when it contacts an operator member 7 projecting upward from the slide point portion 3. The device 9 operates the up controller 24 to stop the ascending slide (closing) 8 at the upper limit. The device 9 responds to actuation of its limit switch to send a signal (SPS) to the up controller 24. A device 10 for confirming that the slide 8 has reached a lower limit is also formed as a limit switch and operates when it contacts another operator member 7a projecting downward from the slide point portion 3, and this device 10 is adapted to operate the down controller 22 to stop the descending slide 8 at the lower limit. The device 10 responds to actuation (closing) of its limit switch to send a signal (SPS) to the down controller 22.
When the limit switch of the device 9 or 10 is closed and sends the signal (SPS), the slide 8 is stopped by the controller 22 or 24 at either the upper limit or the lower limit, respectively.
Then, if the slide adjustment button means 23a is turned ON (actuated), the controller 22 or 24 operates based on the value (die height) set in the slide position setting means 21 (which may be formed as a digital switch), thereby automatically stopping the slide 8 at a position corresponding to the set die height.
A detector 26 for detecting the current (instantaneous) slide position, or a multi-rotating absolute encoder, is adapted to rotate by a drive shaft 12b via a gear mechanism 13 which includes gears 13a and 13b. The detector 26 comprises a reversible counter, a display, and a switch mechanism, and it digitally displays the instantaneous slide position. The switch mechanism, in accordance with Article 31 of the Japanese standards for structure of power press machines, sends signals HLS and LLS to prevent the slide from going beyond the upper and lower limits, respectively. Each signal is emitted upon closing of the upper or lower limit setting means incorporated in the switch mechanism.
The automatic slide adjustment device according to the prior art has the above-described sophisticated construction. However, it cannot satisfy current demands for diversification in forms of production, automatic speed-up and highly precise production in the case of manufacturing various products in small quantities by one press machine or in the case of forming large products.
According to the prior art, generally while the press is stopped, the slide is moved up and down for adjustment to the die height desired during the continuous running of the press. However, in a press having a number of dies disposed in a direction of transfer of the workpieces through the press, a so-called transfer press, the change in the number of dies under load will inevitably cause elongation of the press frame including the column, thereby changing the die height at bottom dead center. Thus, the workpieces formed by the prior art press machine during its initial operation, i.e. during the transition from the start of operation to the continuous running condition while the number of dies under load is continuously changing, those articles formed just prior to the end of the operation, i.e during the transition from the continuous running condition to completion, are treated as defective products. Thus, the prior art not only causes waste and therefore a high production cost but also creates an obstacle to a speed-up of the operation due to its long starting and ending periods. These disadvantages are particularly serious problems for a large press having many dies.
It may be possible to adjust the slide manually each time there is a change in the number of dies under load during successive press cycles of the starting and completion operations. However, because the correct operation of the slide position setting means 21 must rely upon the human operator's memory, the prior art is not only complicated in operation but also likely to cause human error such as a simple mistake in identifying and inputting data relating to the dies in use, thereby possibly resulting in a failure of the dies.